The components of high-temperature mechanical systems, such as, for example, gas-turbine engines, must operate in severe environments. For example, the high-pressure turbine blades, vanes, blade tracks and blade shrouds exposed to hot gases in commercial aeronautical engines typically experience metal surface temperatures of about 1000° C., with short-term peaks as high as 1100° C.
Components of high-temperature mechanical systems may include a Ni- or Co-based superalloy substrate or a ceramic-based substrate, such as a ceramic matrix composite. The substrate can be coated with a thermal barrier coating (TBC), an environmental barrier coating (EBC), or both to reduce surface temperatures. The TBC, EBC, or both may allow use of the component at higher temperatures, which may improve efficiency of the high-temperature mechanical system.
In addition to raising the inlet temperature, gas turbine power and efficiency also may be improved by reducing the clearance between a gas turbine blade and a surrounding blade track or blade shroud. One method of reducing the clearance between blade and track or shroud includes coating the blade track or blade shroud with an abradable coating. As the turbine blade rotates, the tip of the turbine blade may contact the abradable coating and wear away a portion of the coating to form a groove in the abradable coating corresponding to the path of the turbine blade. The intimate fit between the blade and abradable coating provides a seal, which may reduce or eliminate leakage of gas around the blade tip and increase the efficiency of the gas turbine engine by up to 5% in some cases.